In medical diagnosis and treatment of a subject, and in athletic monitoring of a subject, it is often necessary to assess one or more physiological or performance characteristics or symptoms associated with the subject. Athletic performance and progress are often evaluated by examining changes in physiological and/or performance characteristics. Respiratory air volume and other respiratory characteristics can be useful to assess athletic performance, for example, by aiding in detection of changes in physiological state and/or performance characteristics. A key respiratory characteristic is respiratory air volume (or tidal volume).
Monitoring physiological and performance parameters of a subject can be important in planning and evaluating athletic training and activity. A subject may exercise or otherwise engage in athletic activity for a variety of reasons, including, for example, to maintain or achieve a level of fitness, to prepare for or engage in competition, and for enjoyment. The subject may have a training program tailored to his or her fitness level and designed to help him or her progress toward a fitness or exercise goal. Physiological and performance parameters of a subject can provide useful information about the subject's progression in a training program, or about the athletic performance of the subject. In order to accurately appraise the subject's fitness level or progress toward a goal, it may be useful to determine, monitor, and record various physiological or performance parameters, and related contextual information.
Various methods and systems utilizing heart rate have been introduced to approximate effort and physiological stress during exercise. Convenient, practicable, and comfortable means of measuring pulmonary ventilation in non-laboratory conditions, however, have been scarce. While of good value, heart rate can only give an approximation as to the true physiological state of an athlete or medical patient, as it can be confounded by external factors including, for example, sleep levels, caffeine, depressants, beta blockers, stress levels, hydration status, temperature, etc. Furthermore, accurate use of heart rate to gauge physiological performance requires knowledge of the amount of blood flowing to the muscles, which in turn requires knowledge of the instantaneous stroke volume of the heart as well as the rate of pumping. These parameters can be difficult to determine while a subject is engaging in a physical activity.
In addition, chronic diseases are often expressed by episodic worsening of clinical symptoms. Preventive treatment of chronic diseases may reduce the overall dosage of required medication and associated side effects, and may lower mortality and morbidity. Generally, preventive treatment should be initiated or intensified as soon as the earliest clinical symptoms are detected, in order to prevent progression and worsening of the clinical episode and to stop and reverse the pathophysiological process.
Many chronic diseases cause systemic changes in vital signs, such as, for example, breathing and heartbeat patterns, through a variety of physiological mechanisms. For example, common respiratory disorders, such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), are direct modifiers of breathing and/or heartbeat patterns. Other chronic diseases, such as diabetes, epilepsy, and certain heart conditions (e.g., congestive heart failure (CHF)), are also known to modify cardiac and breathing activity. In the case of certain heart conditions, such modifications typically occur because of pathophysiologies related to fluid retention and general cardiovascular insufficiency. Other signs, such as coughing and sleep restlessness, are also known to be of importance in some clinical situations.
Many chronic diseases induce systemic effects on vital signs. For example, some chronic diseases interfere with normal breathing and cardiac processes during wakefulness and sleep, causing abnormal breathing and heartbeat patterns.
Breathing and heartbeat patterns may be modified via various direct and indirect physiological mechanisms, resulting in abnormal patterns related to the cause of modification. Some respiratory diseases (e.g., asthma) and some heart conditions (e.g., CHF) are direct breathing modifiers. Other metabolic abnormalities (e.g., hypoglycemia and other neurological pathologies affecting autonomic nervous system activity) are indirect breathing modifiers.
Asthma is a chronic disease with no known cure. Substantial alleviation of asthma symptoms is, however, possible via preventive therapy, such as the use of bronchodilators and anti-inflammatory agents. Asthma management presents a serious challenge to the patient and physician as preventive therapies may require constant monitoring of lung function and corresponding adaptation of medication type and dosage.
Asthma episodes usually develop over a period of several days, although they may sometimes seem to appear unexpectedly. The gradual onset of the asthmatic episode provides an opportunity to start countermeasures to stop and reverse the inflammatory process. Early treatment at the pre-episode stage may reduce the clinical episode manifestation considerably, and may even prevent the transition from the pre-clinical stage to a clinical episode altogether.
Two techniques are generally used for asthma monitoring. The first technique, spirometry, evaluates lung function using a spirometer (i.e., an instrument that measures the volume of air inhaled and exhaled by the lungs). Airflow dynamics are measured during a forceful, coordinated inhalation and exhalation effort by the patient into a mouthpiece connected via a tube to the spirometer. A peak-flow meter is a simpler device that is similar to the spirometer, and is used in a similar manner.
The second technique evaluates lung function by measuring nitric-oxide concentration using a dedicated nitric-oxide monitor. The patient breathes into a mouthpiece connected via a tube to the monitor.
Efficient asthma management may require daily monitoring of respiratory function, which is generally impractical, particularly in non-clinical or home environments. Peak-flow meters and nitric-oxide monitors provide a general indication of the status of lung function; however, these monitoring devices do not possess predictive value, and are used as during-episode markers. In addition, peak-flow meters and nitric-oxide monitors require active participation of the patient, which is difficult to obtain from many children and substantially impossible to obtain from infants.
CHF is a condition in which the heart is weakened and unable to circulate blood to meet the body's needs. The subsequent buildup of fluids in the legs, kidneys, and lungs characterizes the condition as congestive. The weakening may be associated with either the left, right, or both sides of the heart, with different etiologies and treatments associated with each type. In most cases, it is the left side of the heart that fails, so that it is unable to efficiently pump blood to the systemic circulation. The ensuing fluid congestion of the lungs results in changes in respiration, including alterations in rate and/or pattern, accompanied by increased difficulty in breathing and tachypnea.
Quantification of such abnormal breathing provides a basis for assessing CHF progression. For example, Cheyne-Stokes Respiration (CSR) is a breathing pattern characterized by rhythmic oscillation of tidal volume with regularly recurring periods of alternating apnea and hyperapnea. While CSR may be observed in a number of different pathologies (e.g., encephalitis, cerebral circulatory disturbances, and lesions of the bulbar center of respiration), it has also been recognized as an independent risk factor for worsening heart failure and reduced survival in patients with CHF.
In CHF, CSR is associated with frequent awakening that fragments sleep, and with concomitant sympathetic activation, both of which may worsen CHF. Other abnormal breathing patterns may involve periodic breathing, prolonged expiration or inspiration, or gradual changes in respiration rate usually leading to tachypnea.
Pulsus paradoxus is a physical sign present in a variety of cardiac and extra-cardiac conditions, and is of valuable diagnostic and prognostic significance. Pulsus paradoxus is generally defined as a fall in systolic blood pressure of over 10 mmHg during inspiration. Pulsus paradoxus has been associated with the following conditions: cardiac tamponade, pericardial effusion, constrictive pericarditis, restrictive cardiomyopathy, pulmonary embolism, acute myocardial infarction, cardiogenic shock, bronchial asthma, tension pneumothorax, anaphylactic shock, volvulus of the stomach, diaphragmatic hernia, and superior vena cava obstruction.
In bronchial asthma, pulsus paradoxus is of significance because it has often been associated with mild obstructions and can therefore serve as an early warning sign.
Various systems and methods have thus been developed to obtain and transmit physiological and contextual information associated with a subject to a monitoring station.
U.S. Pat. No. 6,468,234, issued Oct. 22, 2002, describes an apparatus for measuring sleep quality that utilizes sensors incorporated in a sheet that is laid on top of a conventional mattress on which the subject sleeps. The sensors collect information, such as the subject's position, temperature, sound/vibration/movement, and optionally other physical properties.
The apparatus includes one or more layers of arrays of integrated sensors, which can be incorporated in layer pads and then placed on a conventional mattress, one or more controllers coupled with the arrays of integrated sensors in each layer pad for the purpose of acquiring data from the sensors, real-time analysis software for analyzing data acquired by the controller from the array of integrated sensors, interface software for collecting user lifestyle data, lifestyle correlation software for correlating the lifestyle data with the data acquired by the array of sensors, and one or more active components to improve sleep quality based on the data acquired through the sensors and the lifestyle data. The array of sensors provides one or more of the following data: position, temperature, sound, vibration, and movement data.
U.S. Pat. No. 6,840,907, issued Jan. 11, 2005, describes a respiratory analysis system for monitoring a respiratory variable of a patient. The system includes a sensor array for accommodating a patient in contact therewith and a processing means. The array has a plurality of independent like sensors for measuring respiratory movement at different locations on the patient to generate a set of independent respiratory movement signals. The processing means receives and processes the movement signals to derive a classification of individual breaths using, for each breath, the respective phase and/or amplitude of each movement sensor signal within the set for that breath.
U.S. Pat. No. 6,517,497, issued Feb. 11, 2003, describes techniques for monitoring and/or quantitatively measuring a patient's respiration using a flexible piezoelectric film sensor. The apparatus includes a piezoelectric film that converts acoustical waves generated by the patient's respiration into electrical signals. The piezoelectric film sensor can be used to monitor the respiration of a patient by correlating the sound generated in the patient's airway with respiratory activity. The data generated by the sensor may be further analyzed by a patient monitor to diagnose respiratory conditions.
U.S. Pat. No. 5,002,060, issued Mar. 26, 1991, describes a monitoring system adapted to simultaneously monitor cardiac and respiratory rates and characteristics and substantial changes in temperature of a subject. The system uses sensors which are passive and non-invasive, and located remotely from (i.e., completely off of) the subject. Sensor signals are processed in order to provide an alarm accompanied with displayed indication of any irregularities in the cardiac and respiratory rates and characteristics, and substantial changes in temperature.
U.S. Pat. No. 6,450,957, issued Sep. 17, 2002, describes a respiration monitoring system that monitors the state of disorder of the respiratory system of a sleeping patient based on the detection of respiratory body movement, without the need to put sensors directly on the patient's body. The system includes weight sensors that produce weight signals attributable to the patient's respiratory body movement. From weight signals having a frequency band of respiration, a respiratory body movement signal is produced. The fall of blood oxygen saturation, which occurs during obstructive apnea of the sleeping patient, is determined based on the variation pattern of the amplitude of the respiratory body movement signal.
U.S. Pat. No. 6,790,183, issued Sep. 14, 2004, describes a lung sound diagnostic system for use in collecting, organizing, and analyzing lung sounds associated with the inspiration(s) and expiration(s) of a patient. The system includes a plurality of transducers that may be placed at various sites around the patient's chest. The microphones are coupled to signal processing circuitry and A/D converters that digitize the data and preferably provide the digital data to a computer station. The system may also include application programs for detecting and classifying abnormal sounds. Additionally, the system may include an analysis program for comparing selected criteria corresponding to the detected abnormal sounds with predefined thresholds in order to provide a likely diagnosis. Also described are a system and method for differentiating between the crackles produced by a patient with interstitial pulmonary fibrosis (IPF) from the crackles produced by a CHF patient.
U.S. Pat. No. 5,738,102, issued Apr. 14, 1998, describes a system for monitoring and computer analyzing select physiological variables of a patient in real time in order to alert medical personnel to the need for medical treatment or to automatically administer such treatment under computer control. The physiological variables monitored by the system may include lung sounds, respiratory rate and rhythm, heart rate and rhythm, heart sounds, and body temperature. Coded signals relating to the physiological variables are produced and compared with reference versions of same by a decision computer in order to evaluate the patient's condition. If the evaluation indicates medical treatment is needed, the decision computer activates a local and/or a remote alarm to alert medical personnel and/or activates one or more actuators for administering a medical treatment such as the injection or infusion of a drug.
Examples of body sounds that may be detected are respiratory sounds and heart sounds. In the case of the former, the computer produces coded signals representing the rate and rhythm of breathing derived from the respiratory sounds.
The system is described as being able to detect abnormal breathing patterns such as apnea, tachypnea, hyperpnea (e.g., Kussmaul breathing associated with metabolic acidosis), bradypnea, Cheyne-Stokes breathing, ataxic breathing, and obstructive breathing. Coded signals may also be generated from the respiratory sounds that indicate the presence of added lung sounds such as rales associated with pneumonia and pulmonary edema, wheezes associated with obstructive lung disease, and pleural rubs due to inflammation of the pleural membranes.
U.S. Pat. No. 6,599,251, issued Jul. 29, 2003, describes non-invasive techniques for monitoring the blood pressure of a subject. A pulse signal is detected at both a first and second location on the subject's body. The elapsed time between the arrival of corresponding points of the pulse signal at the first and second locations is determined. Blood pressure is related to the elapsed time by mathematical relationships.
U.S. Patent Application Publication No. 2004/0133079, published Jul. 8, 2004, describes techniques for predicting patient health and patient relative well-being within a patient management system. One embodiment utilizes an implantable medical device including an analysis component and a sensing component further including a three-dimensional accelerometer, a transthoracic impedance sensor, a cardio-activity sensor, an oxygen saturation sensor, and a blood glucose sensor. One analysis described is detecting changes in transthoracic impedance variation patterns that are indicative of the early occurrence of a new disease state (such as Chronic Obstructive Pulmonary Disease), the onset of an illness (such as asthma), or the progression of a disease (such as DC impedance indicating lung fluid accumulation that corresponds to the progression of heart failure).
U.S. Pat. No. 6,454,719, issued Sep. 24, 2002, describes techniques for determining the cardiac condition of a patient by a cardiac monitor apparatus using a respiration parameter such as a current respiration signal or a respiration rate. The variability of the respiration parameter is used to generate a signal indicative of the current heart failure status of the patient, and, more particularly, whether the patient's condition has improved, worsened, or remained unchanged over a predetermined time period. The circuitry for detecting the respiration parameter may be implanted in the patient, for example as part of a pacemaker, while at least some of the analyzing circuitry may be external and remote from the patient. Alternatively the whole device may be implantable.
U.S. Pat. No. 6,600,949, issued Jul. 29, 2003, describes a method for monitoring the condition of a heart failure patient using respiration patterns. An implantable or other ambulatory monitor senses the patient's respiratory patterns to identify the presence of periodic breathing or Cheyne-Stokes respiration. In a first embodiment, mechanical changes of the thorax due to breathing are detected and this data is used to recognize hyperventilation and apnea or hypoventilation. In a second embodiment, Cheyne-Stokes respiration is recognized by detecting changes in blood or tissue pH or CO2 concentration and partial pressure. In another embodiment, changes in pulse amplitude associated with Cheyne-Stokes respiration are detected. Alternating loss and return of respiration-induced amplitude modulation or pulse-interval variation may also be used to identify the presence of Cheyne-Stokes respiration.
In yet another embodiment, modulation of the average heart rate over time is monitored and its absence is used as an indicator of Cheyne-Stokes respiration. This information may be used to warn the patient or healthcare provider of changes in the patient's condition warranting attention.
U.S. Pat. No. 6,527,729, issued Mar. 4, 2003, describes a method for monitoring the disease progression of a heart failure patient. An implantable or other ambulatory monitor senses acoustic signals, including heart and lung sounds within the patient. Significant changes in the energy content of either the heart or lung sounds is indicative of a heart failure exacerbation.
U.S. Pat. No. 6,015,388, issued Jan. 18, 2000, to Sackner et al. (VivoMetrics, Inc.) describes a method for measuring respiratory drive, including determining a peak inspiratory flow and a peak inspiratory acceleration from a breath waveform derived from rib cage motion and abdominal motion using a plethysmograph or other external respiratory measuring device. The respiratory drive is ascertainable even during complete blockage of the respiratory system. In one embodiment, the peak inspiratory drive is used to initiate inspiration in a mechanical ventilator and for determining an index describing a shape of the waveform for controlling a continuous positive air pressure (CPAP) device.
U.S. Pat. No. 6,047,203, issued Apr. 4, 2000, to Sackner et al. (VivoMetrics, Inc.) describes physiological monitoring apparel worn by a monitored individual, the apparel having attached sensors for monitoring parameters reflecting pulmonary function, cardiac function, or the function of other organ systems. In one embodiment, an alarm is generated based on a trend progressing over one to a few hours.
There are several drawbacks associated with the noted prior art systems and methods. A major drawback is that prior art systems and associated methods have limited means for transmitting signals acquired from a medical patient or athlete to a monitoring station.